Devices for generating and dispensing foams by manual compression of a reservoir, bulb, or bellows are well known. The compression typically forces air and foamable liquid from a reservoir into a mixing chamber where they mix to produce a foam before being dispensed from the device. Such devices are disclosed in a series of patents and patent applications of H. Earl Wright: U.S. Pat. No. 3,428,222, issued Feb. 18, 1969; U.S. Pat. No. 3,709,437, issued Jan. 9, 1973; U.S. Pat. No. 3,937,364, issued Feb. 10, 1976; U.S. Pat. No. 4,018,364, issued Apr. 19, 1977; U.S. Pat. No. 4,184,615, issued Jan. 22, 1980; U.S. Pat. No. 4,531,659, issued Jul. 30, 1985; U.S. Pat. No. 4,880,161, issued Nov. 14, 1989; and U.S. patent application Ser. No. 07/869,861, filed Apr. 16, 1992; now U.S. Pat. No. 5,219,102; each of which is incorporated by reference.
Most prior art foaming devices, including those disclosed in the Wright patents and patent applications, share a number of common elements. Each foamer contains a reservoir for storing the foamable liquid and a quantity of air, and further contains a means for supplying compressed air. The reservoir itself may be manually compressible or a separate, compressible air supplying means may be connected to the reservoir. Each foamer contains a mixing chamber where the foamable liquid and air mix to form the foam. Each contains a restricted passage for the flow of air to the mixing chamber. Each contains a passage from the liquid reservoir to the mixing chamber, typically a vertical dip tube. And each contains some means for dispensing foam from the mixing chamber. As mentioned above, these foamers are all operated by compressing the air supplying means which, in turn, forces air and foamable liquid into the mixing chamber. When the air supplying means is released, the vacuum created thereby draws air and undispensed foam from within the device back into the reservoir.
The ratio of foamable liquid to air supplied to the mixing chamber is critical to foam formation in these devices. If the ratio is too high, the foam is too wet. If the ratio is too low, the foam is too dry. Because of the importance of this ratio, many of the foamers disclosed in the Wright patents and patent applications are specifically designed to maintain a relatively constant liquid-to-air ratio. For example, the foamer disclosed in U.S. patent application Ser. No. 07/869,861 now U.S. Pat. No. 869,861, separates returning foam from the air passage inlet to prevent foam from entering the air passage (and thereby making the dispensed foam too wet) if the foamer is compressed again without delay. As another example, the foamer disclosed in U.S. Pat. No. 4,880,161 employs a flexible diaphragm to independently meter the liquid and air to the mixing chamber.
While the Wright foamers have enjoyed great commercial success, they all exhibit a lag from the time the reservoir is compressed to the time the foam having the desired liquid-to-air ratio is dispensed. In the Wright foamers of the upright type, the initial compression first produces the expulsion of air, rather than foam, because it takes some amount of time for the liquid to rise up the vertical dip tube, pass through the mixing chamber, and exit the device. This also results in the initial foam dispensed being on the dry side.
It would be desirable for a foaming device to produce foam having the desired liquid-to-air ratio immediately upon compression of the air supplying means. However, none of the foamers shown in the prior art exhibits this characteristic.